Manhole assemblies have been found to experience significant interior corrosion and deterioriation even in cases where high acidic effluents that are known to be harmful to sewers and sewer treatment are prohibited from entering the sewers without first being dissipated or neutralized. Nevertheless, hydrogen sulfide which is inherent in sewerage is developed due to the presence of sulfur compounds such as sulfate, sulfite or other inorganic or organic sulfur. The last mentioned compounds are reduced to sulfide by sulfate-reducing bacteria normally found in the effluent. The generation of hydrogen sulfide is accelerated when high temperatures and low flow rates are encountered. The useful life of concrete is determined by dividing the available effective thickness of the concrete by the corrosion rate which corrosion rate can be calculated when all factors are known. The effective thickness of the concrete is the amount covering the steel reinforcement embedded therein.
Coatings have been applied to manhole interiors but have been found to have a poor track record. For example, although coal tar epoxy provides effective protection against hydrogen sulfide, the coatings have provided poor field performance due to application difficulties.
As a result, linings of plastic material, such as polyvinylchloride (PVC), provide the best performance for interior corrosion protection against hydrogen sulfide. Such plastic linings are further compatible with plastic pipe now being used extensively in sanitary systems. To date, however, it is extremely difficult to fabricate interior linings and integrate such interior linings into vertical structure and particularly manhole assemblies. Flexible type linings are presently used in pipes covering the upper 270 degrees of the pipe interior. This is the portion attached by the H.sub.2 S generated from sewerage. This flexible material is not easily used on manholes which requires 360 degrees protection for the manhole interior.